WASHINGTON — K. T. McFarland, the former Fox News commentator appointed by President Trump as deputy national security adviser, is expected to leave that position soon and may be nominated to be the United States ambassador to Singapore, according to officials briefed on the matter.

Ms. McFarland’s departure had been seen as likely since the forced resignation of Michael T. Flynn, the retired three-star general who was Mr. Trump’s first national security adviser. Mr. Flynn’s successor, Lt. Gen. H. R. McMaster, has been moving to put a more traditionally professional stamp on the operations of the National Security Council.

Last week, Mr. Trump signed an order restructuring the council’s “principals committee” along more traditional lines than the version he had initially put in place. It removed Stephen K. Bannon, the White House’s chief strategist and a former chairman of the conservative website Breitbart, while adding several officials Mr. Trump’s original order had left off, including the chairman of the Joint Chiefs of Staff and the directors of national intelligence and the C.I.A.

Administration officials briefed on the matter confirmed Ms. McFarland was stepping down, but said her departure would not be immediate. The officials also said her possible nomination for the ambassadorship to Singapore, while likely, had not been finalized.

Ms. McFarland’s style had grated against some of the professional staff members on the National Security Council, which sees itself as apolitical. For example, while addressing the staff at a meeting after Mr. Flynn’s ouster, Ms. McFarland noted that she was wearing shoes from Ivanka Trump’s brand, according to an official who was present.

At an earlier meeting about two weeks into the administration, Ms. McFarland invoked Mr. Trump’s campaign slogan, telling the assembled group of career staff members, most of whom had been in the same roles during the Obama administration, that they needed to “make America great again.”

It was not clear whether Dina Powell, whom General McMaster brought in as deputy national security adviser for strategy, would succeed Ms. McFarland as the principal deputy. The official in that role leads interagency “deputies committee” meetings in the Situation Room involving the No. 2 officials from national security agencies and government departments.

Ms. Powell, an assistant secretary of state for education and cultural affairs in the Bush administration, is fluent in Arabic and was previously the president of the Goldman Sachs Foundation. She was the only woman in the widely distributed photograph of Mr. Trump and his aides receiving a briefing about the recent airstrike on Syria at his resort in Florida.

Ms. McFarland, 65, worked as an aide on the National Security Council in the Nixon and Ford administrations, and served as a Pentagon speechwriter and spokeswoman in the Reagan administration. In more recent years, she was known for her criticism on Fox News of President Barack Obama’s handling of national security policy. In September 2014, after the Islamic State swept out of Syria to conquer swaths of Iraq and killing two kidnapped Americans, she said on Fox News that Mr. Obama was guilty of “dereliction of duty” because he “was playing a lot of golf this summer, but he was clearly not attending to the defense of the United States.”

At the same meeting where Ms. McFarland told staff members to “make America great again,” Mr. Flynn talked to them about using their time at the council to gain experience to help them in other parts of the government. He then asked for a show of hands to see how many expected to be working at the White House in a year.

Mr. Flynn, according to people present, then turned to Ms. McFarland and, in an apparent self-deprecating joke, said, “I wonder if we’ll be here a year from now?”